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  • 1
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The photoinduced formation of oligomers in single crystals of 2,5-distyrylpyrazine (DSP) was investigated by X-ray and electron diffraction techniques and also by gel permeation chromatography (GPC). The DSP crystals were characterized for the presence and nature of dislocations by dark-field images and etch-pit studies. Small angle grain boundaries were identified to be the prominent feature, but in general the crystals were highly perfect. A correlation between the sites of the defects and the formation of the photoproduct could not be detected. The oligomers formed in a solid-solution under appropriate irradiation conditions. Thus, DSP oligomer of number average degree of polymerization P̄n = 3,2 in macroscopic single crystal texture was obtained for the first time using a laser light source at 478 nm. Deterioration of the single crystal texture of DSP usually observed during photopolymerization is explained as being caused by inhomogeneous light distribution which in turn causes an inhomogeneous product distribution with accumulation of large strain fields. These can be made visible by the multiplication of etch pits. Phase separation between oligomer and polymer is observed on further irradiation of the oligomer single crystals. The oligomer phase seems to play the role of an intermediate in the photopolymerization of DSP at wavelengths λ 〈 400 nm. The molecular weight distribution of the oligomers was studied by GPC. The data are only compatible with the assumption that the rate constant of dimerization is higher than that for the addition of a monomer to an already existing oligomer.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 31 (1993), S. 2959-2968 
    ISSN: 0887-624X
    Keywords: aluminoxanes ; metallocene catalysts, supported ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of methylaluminoxane (MAO) with 1,6-hexanediol or 1,10-decanediol leads to white powdery materials which were studied by 13C and 27Al MAS NMR, scanning electron microscopy (SEM), and whose surface area and porosity was determined according to the BET method. The hydrolysis of trimethylaluminum with hydrogel was carried out and the product was investigated by SEM. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 131 (1985), S. 107-115 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Verträglichkeit von 17 Kautschukmischungen wurde mit Hilfe von drei verschiedenen Methoden bestimmt: Phasentrennung, Messung der Glasübergangstemperaturen und Elektronenmikroskopie. Der Einfluß von Strukturdetails (Seitenketten, Konfiguration der Doppelbindungen, sowie deren Abstand voneinander) auf die Verträglichkeit wurde untersucht. Die Meßergebnisse können wie folgt interpretiert werden:Seitenketten haben den stärksten Einfluß auf die Verträglichkeit. Polyisobutylen und Polypentenamer sind z. B. miteinander nicht verträglich. Nicht so starken Einfluß hat die Konfiguration der Doppelbindungen in der Polymerkette. Polymere mit gleicher Konfiguration sind verträglicher als solche mit verschiedener Konfiguration. Den geringsten Einfluß hat der Abstand der Doppelbindungen entlang der Polymerkette. Polyoctenamer und Polypentenamer mit 6 bzw. 3 Methylengruppen zwischen den Doppelbindungen sind z. B. weniger verträglich als Polybutadien und Polypentenamer mit 2 bzw. 3 Methylengruppen).Cis-Polypentenamer und Naturkautschuk erwiesen sich als gut verträglich, obwohl elektronenmikroskopische Aufnahmen Domänen mit einer durchschnittlichen Größe von SO Å zeigen.
    Notes: Compatibility of 17 pairs of rubbers has been investigated by means of phase separation, glass transition measurements and electron microscopy. Influence of structural details like side chains, configuration of monomer units and distance between double bonds in the chain on the compatibility of polymers has been elucidated. Experimental data lead to following results:Side chains have the strongest influence on compatibility; poly(isobutene) and poly(pentenamer), e.g., are highly incompatible. With decreasing influence on compatibility follows the configuration of the double bond in the polymer chain. Polymers with equal configuration are more compatible than polymers with different configuration. The structural detail with the weakest influence on compatibility is the distance between double bonds along the polymer chain. Poly(octenamer) and poly(pentenamer), e.g., with 6 and 3 methylene groups between the double bonds are less compatible than poly(butadiene) and poly(pentenamer) with a distance of 2 and 3 methylene groups.Cis-poly(pentenamer) and natural rubber were found to be highly compatible although electron micrographs show domains with an average diameter of 50 Å.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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